"We consider this to be a serious and grave threat to our national security," U.S. Attorney Stephen Murphy III of Detroit said Tuesday in announcing the arrests.

All four men were charged with conspiring to violate the U.S. Arms Export Control Act, which is punishable by up to 5 years in prison and a $250,000 fine. Court papers did not indicate reasons for the purchase or what the men intended to do with the weapons.

The four were arrested Sunday after meeting in Hawaii with people they thought were representing a Detroit-area company, which authorities say the men believed would provide the military hardware. It was to be shipped to Indonesia through Singapore.

An indictment in Detroit identified Djuliarso and Amran as owners of four businesses located in or doing business in Indonesia and Singapore. Soeharli financed the purchases and Beecroft attended the meeting in Hawaii to arrange shipment of the items, according to court papers.

Djuliarso and Amran also were charged with violating export law and money laundering.